1. Field of the Invention
The present invention relates to a head stock for selective use between dead and live center drives of a spindle in a grinding machine.
2. Description of the Prior Art
In the grinding operation with a grinding machine, it is usual to use the dead center drive for working a workpiece held by centers and to use the live center drive for working a workpiece having a large center opening or a workpiece held by a chuck. For this reason, in a grinding machine, such as a universal grinding machine, adapted to perform both inner and outer grinding operations, the head stock is constructed such that the drive of the workpiece can be readily switched between the live center drive and the dead center drive.
A conventional head stock for switching the drive between the live center and the dead center drive is shown in FIGS. 1 and 2 of the drawings. Therein, a spindle 3 holding a center 2 and a pulley 4 coaxial with the spindle 3 are rotatably mounted within a head stock housing 1. The pulley 4 is driven by belts connected to a transmission for reducing the rotation of a motor. At the end surface of the pulley 4 are secured a face plate 5 having a dog 5a for rotating a workpiece and a claw 6, adjustable in a radial direction. A recess 7, associated with the claw 6, is formed on the outer periphery of a spindle 3. A switching pin 8 is movably received in the head stock housing 1. An engaging groove 9, engageable with the switching 8, is formed on the spindle 3. For the dead center drive, the claw 6 is moved out of engagement with the recess 7 and the switching pin 8 is moved into engagement with the groove 9, as shown in FIG. 1, whereas for the live center drive, the claw 6 is moved into engagement with the recess 7 and the switching pin 8 is removed from engagement with the groove 9.
In order to perform the chucking operation, the face plate 5, secured to the end surface of the pulley 4, and the center 2 are removed and a chuck 11 is secured to the end surface of the spindle 3, through a face plate 10, as shown in FIG. 2. At the same time, the claw 6 is moved into engagement with the recess 7 and the switching pin 8 is moved away from the groove 9 of the spindle 3.
In this manner, the drive for the spindle 3 can be changed between the dead and live center drives. However, in the conventional device of this type, two operations are required for the claw 6 and the switching pin 8, and the operator may forget one of these operations. In particular, since the claw 6 is usually made invisible by the existence of the face plate 5, the operator may fail to operate the same, to thereby cause the often occurring trouble.
In the chucking operation, the connection between the pulley 4 and the spindle 3 is accomplished by the claw 6. However, the claw 6 cannot be operated as long as the face plate 10 is secured. Furthermore, since the pulley 4 is connected to the motor through the transmission, it is difficult to rotate the chuck by a manual operation.